1. Field of Invention
The present invention relates to a continuously variable valve timing apparatus (CVVT).
2. Description of Related Art
An internal combustion engine is an apparatus that generates power by burning fuel with intake air in a combustion chamber. Such an internal combustion engine is provided with intake valves to take in the air and fuel and exhaust valves to exhaust combustion gas from the combustion chamber. The intake valves and exhaust valves are operated by rotation of camshaft driven by the rotation of crankshaft.
Optimal timing of the intake and exhaust valves depends on various factors such as an engine speed and engine load. In such background, a variable valve timing (VVT) apparatus has been developed so that the camshaft is not fixedly but variably operated by the crankshaft depending on engine driving circumstances.
A continuously variable valve timing (CVVT) apparatus, which is an advanced type of variable valve timing (VVT) apparatus, has been developed to control the valve timing at an arbitrary value within a predetermined range.
Various schemes of a CVVT apparatus that are hydraulically or electrically controlled fail to provide a self-locking function, that is, a function that the target valve timing may be locked without substantially consuming control power. This means that substantial amount of electrical or hydraulic energy is consumed to maintain a target valve timing.
In addition, precise control of a cam angle becomes difficult because the CVVT apparatus typically uses a plurality of gears and grooves in which case tolerances of many components accumulatively add the difficulty. In addition, when gears are used in the CVVT apparatus, noise problem has been easily raised by backlash, which in turn results in the loss of durability.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.